1. Structures, Unions, and Enumerations Chapter 16

2. 2 Data Structure ( 資料結構 ) Content of data –Attributes of an object Person:name, age, sex, … A poker card:suit ( 花色 ), face ( 點數 ) –Columns of a record Book-Borrowing:book_title, book_ID, borrower, date It is convenient if we can save them in a structure. –data structure ( 資料結構 )

3. 3 Structure Types (16.2) Syntax: struct structureName{ dataType member1; dataType member2;... };  Ex: struct personData{ char name[20]; int age; bool sex; }; A pair of curve parentheses NOTE!! Ended with ;

4. 4 Structure Variables (16.1) struct defines a new variable type ( 資料 型態 ), not a new variable. We can use a defined structure type to define variables. Ex:  personData player1, player2;  personData student[10];

5. 5 Declaring Structure Variables  struct personData{ char name[20]; int age; bool sex; };  personData player1, player2; player1player2

6. 6 Declaring Structure Variables  struct personData{ char name[20]; int age; bool sex; };  personData player1 = {" 莊孝維 ", 19, false}, player2 = {" 林志零 ", 20, true}; player1player2 agesex name agesex name members; fields records

7. 7 Declaring Structure Array (16.3)  personData student[10]; student[0]student[9] ‧‧‧ student[] student[1]

8. 8 Initializing When Defining (16.3) Ex: personData student[10]={ {" 莊孝維 ", 19, false}, // student[0] {" 林志零 ", 20, true}, // student[1]... //name,age,sex }; The initial data are given in the order of members in the structure and the order of elements in the array.

9. 9 Declaring Structure Variables The following statements are also legal:  struct personData a1,student[10];  struct info{ int a,b; } info1, info2;  struct { int a,b; } info1, info2; define variables immediately after the definition of a structure

10. 10 Accessing Members of Structure '.' : structure member operator (dot operator) player1 player1.name player1.sex player1.age  See ->

11. 11 Accessing Members of Structure '.' : structure member operator (dot operator) –Ex: personData player1; strcpy( player1.name, " 莊孝維 "); player1.age = 19; player1.sex = false; // true for female, false for male player1 agesex name

12. 12 Practice Define a data structure to store data of a student. –What attributes do we need to save? What are their types? Define 100 users. Input some data (not necessary 100) from the keyboard. Print these data out.

13. 13 Pointer to A Structure Ex: personData player1, *mPtr; mPtr = &player1; player1 mPtr

14. 14 Accessing Members of Structure '->' : structure pointer operator (arrow operator) player1 mPtr->name mPtr->sex mPtr->age mPtr  See.

15. 15 Accessing Members of Structure '->' : structure pointer operator (arrow operator) – 例： personData player1, *mPtr=&player1; strcpy(mPtr->name, " 莊孝維 "); mPtr->age = 19; mPtr->sex = false; mPtr player1 agesex name

16. 16 Dot operator has higher preference than dereferencing operator. Accessing Members of Structure personData player1, *mPtr; mPtr = &player1; scanf("%d", &player1.age); scanf("%d", &(player1.age)); printf("%d\n", player1.age); printf("%d\n", mPtr.age); printf("%d\n", mPtr->age); printf("%d\n", (*mPtr).age); printf("%d\n", *mPtr.age);  

17. 17 Pointer to A Structure NOTE!! A pointer is just a variable with 4 bytes. No memory of its reference type will be allocated at definition time. –Hence you have to define a real variable of this type and let pointer refer to it before you use this pointer. Ex: personData *mPtr; personData player1; mPtr = &player1; player1 mPtr

18. 18 Structure Assignment You can assign a variable's content as the other variable's content directly by = if they are of the same structure. struct data{ int age,sex; };  data player1, player2;  player1.age = 34; player1.sex = 1;  player2 = player1; player1player2 age sex 341 1

19. 19 Structure Comparison The same as strings, you cannot compare two variables of the same structure by ==.  For strings (i.e. char *), == means two pointers refer to the same address.  For structures, == is undefined. if (player1 == player2) … Compile error C2676: binary '==' : 'struct person' does not define this operator or a conversion to a type acceptable to the predefined operator

20. 20 Structure Comparison So… –Write a function to compare two variables of the same structure by comparing all the members of the structure.

21. 21 Passing Structure as Parameters myfunc(personData manager);  Note that it is call by value!  If you want to modify the content of the variable, please call by reference. myfunc(personData *manager); __ ↑ use structure name as variable type __ ↑ call by reference

22. 22 Practice Write a function to compare if two personData variables have the same values. Write a function to initialize a personData variable as follows: {" 無名氏 ", 0, true} struct personData{ char name[20]; int age; bool sex; };

23. struct city { char name[20]; int population; double area; }; name areapopulation Taipei name areapopulation Keelung city Taipei = {"Taipei", 2000000}, Keelung = {"Keelung", 200000}; Objects vs. Structures An Example

24. agename birthplacelivingplace struct city { char name[20]; int population; double area; }; struct person { char name[20]; int age; city *birthplace, *livingplace; }; name areapopulation Taipei name areapopulation Keelung person Mary = {"Mary", 32}, Susan = {"Susan", 5}; ? ? Mary agename birthplacelivingplace ?? Susan

25. agename birthplacelivingplace struct city { char name[20]; int population; double area; }; struct person { char name[20]; int age; city *birthplace, *livingplace; }; name areapopulation Taipei name areapopulation Keelung // Mary was born in Keelung and lives in Taipei now Mary.birthplace = &Keelung; Mary.livingplace = &Taipei; ? ? Mary agename birthplacelivingplace ?? Susan

26. agename birthplacelivingplace struct city { char name[20]; int population; double area; }; struct person { char name[20]; int age; city *birthplace, *livingplace; }; name areapopulation Taipei name areapopulation Keelung // Susan lives with Mary Susan.livingplace = Mary.livingplace; Mary agename birthplacelivingplace ?? Susan

27. 27 Nested Structures (16.3) A member of a structure can be a structure of another type. Ex: struct dateData{ int year, month, day; }; struct personData{ char name[20]; dateData birthdate; };  personData mySon; mySon.birthdate.day = 26; mySon name birthdate yearmonthday 26

28. 28 typedef (16.2) To give an alias name –typedef int ageType; ageType age[20]; To give a shorter name for "struct yourStructureName" –typedef struct personData pType; pType student[20]; original name new name original name new name

29. 29 Examples of typedef  typedef int ageType;  typedef struct personData pType;  typedef personData * personPtr;  typedef struct{ char id[13],nickname[100]; int loginTimes,status; } bbsIDdata;